Depends on the PKM tool I would say. I used Joplin with its internal sync with Nextcloud without problems in the past. Then I switched to Logseq which does not have an integrated sync so I had to rely on the respective clients. On Windows and Linux this works fine with Nextcloud, but automatic sync on phones (at least Android) sucks. So I switched to Syncthing for this purpose as the phone sync is more reliable now. I have however a small “server” (RPi or similar is sufficient) running 24/7 to keep the notes in sync even if my devices would not be online in parallel.